This work addresses the optimal design of a flexible heat exchanger network using model based optimization, applied to hydrogen production by means of an ethanol steam reforming process. High efficiencies are obtained at different hydrogen production levels ranging from 25 to 100% of a nominal output. System structure, heat exchanger sizing, and operation conditions are simultaneously settled, ensuring both operational feasibility and optimality. The system involves a reforming reactor, vaporization and reheating equipment, combustors, and a heat exchanger network system. A multi-period nonlinear optimization problem (NLP) was formulated to account for the production level distribution. Equipment sizing constraints and structural constraints link the different scenarios. The trade-off between area and efficiency is analyzed using a multi-objective epsilon constraint approach. Models were developed in the GAMS environment. The resulting solutions, for the maximum area case, maintain alcohol combustion at low levels showing efficiencies around 63% in each operational level. Pareto Optimal diagram shows that a 1% reduction of efficiency allows a 50% decrease in total required heat exchanger area by 50%. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.